Deformation and Fracture of a Particle-Reinforced Aluminum Alloy Composite: Part I. Experiments

摘要

Mechanical tests were performed on a powder-metallurgically processed 7093/SiC/15p discontinuouslyreinforced aluminum (DRA) composite in different heat-treatmentconditions, to determine the influence of matrix characteristics onthe composite response. The work-hardening exponent and thestrain to failure varied inversely to the strength, similar tomonolithic Al alloys, and this dependence was independent of thedominant damage mode. The damage consisted of SiC particlecracks, interface and near-interface debonds, and matrix ruptureinside intense slip bands. Fracture surfaces revealed particlefracture-dominated damage for most of the heat-treatmentconditions, including an overaged (OA) condition that exhibited acombination of precipitates at the interface and a precipitate-freezone (PFZ) in the immediate vicinity. In the highly OA conditionsand in a 450 deg C as-rolled condition, when the compositestrength became less than 400 MPa, near-interface matrix rupturebecame dominant. A combination of a relatively weak matrix and aweak zone around the particle likely contributed to this damagemode over that of particle fracture. Fracture-toughness tests showthat it is important to maintain a proper geometry and testingprocedure to obtain valid fracture-toughness data. Overagedmicrostructures did reveal a recovery of fracture toughness ascompared to the peak-aged (PA) condition, unlike the lack oftoughness recovery reported earlier for a similar 7XKK (Al-Zn-Cu-Mg)-based DRA. The PA material exhibited extensivelocalization of damage and plasticity. The low toughness of theDRA in this PA condition is explored in detail, using fractographyand metallography. The damage and fracture micromechanismsformed the basis for modeling the strength, elongation, toughness,and damage, which are described in Part II of this work.